This invention relates to a cutting tool including a tool body with, on the one hand, a front part for holding a cutting insert and, on the other hand, a rear part, which houses a plurality of nozzles. The nozzles are supplied with pressurized cooling liquid from an external liquid supply source via a duct system inside the tool body for the purpose of spraying a high pressure cooling liquid jet towards the area of an upper surface on the cutting insert in a manner forming an hydraulic wedge between the upper surface of the cutting insert and a chip emanating from a workpiece, in order to lift and distance the chip from the cutting insert.
It is a common practice to cool not only the cutting inserts of cutting tools, e.g. Tools for turning, but also to cool the workpiece (which commonly comprises metal which is to be machined by the tool), as well as to cool the chips which are cut from the workpiece. A fundamental aim in today""s technology for cutting or chip removing machining is to enable the use of as high a pressure as possible in the cooling liquid and to supply this in the form of one or more thin jets confined tightly together which generally are directed towards the cutting insert and the chip cut thereby. The higher the jet pressure, the greater are the possibilities to use the liquid jet in an advantageous way, not only for pure cooling, but also for mechanically affecting the chip cut from the workplace, by applying a force from the jet to the chip, more precisely with the purpose of breaking this chip into smaller pieces and/or guiding the chip away from the tool in a controlled way. Among those skilled in the art, there are different opinions as to what, in this connection, is to be regarded as low and high liquid pressure, respectively. Generally, the classification can, however, be made in following ranges:
Low pressure less than 10 bar,
Intermediate pressure 10-100 bar, and
High-pressure greater than 100 bar.
On older cutting tools, cooling always took place using low pressure cooling liquid, while cutting tools according to somewhat more recent technology have worked with an intermediate pressure cooling liquid. In the more modem technology, liquid pressure of hundreds of bar are sometimes used.
When the cutting insert on a cutting tool, used for, for instance for turning, cuts a chip free from a rotating workpiece, commonly formed of metal, considerable amounts of heat are developed. The cutting of the chip is carried out in a primary shear zone, which is developed in a peripheral portion of the workpiece and extends obliquely upwards/backwards from the cutting edge of the cutting insert. By virtue of the high temperatures which are developed not only in the chip and the workpiece, but also in the cutting insert, the chip separated in the primary shear zone may not slide forward in a manner which is frictionless and without resistance along the upper surface of the cutting insert. On the contrary, the very hot chip may adhere to the upper surface of the cutting insert along a certain contact length in a manner similar to welding. The contact length may, depending on, for instance, the material of the workpiece, vary between tenths of a millimeter and approximately one millimeter extending backwards from a support zone near the cutting edge. In this connection, the hot chip material adheres powerfully as a thin layer above which the real separation of the chip takes place by shearing in a secondary shear zone (frequently called a weld zone). After this, a so called friction zone follows along which the chip is in strong friction contact with the cutting insert before leaving the cutting insert. In order to facilitate the separation of the chip from the cutting insert, most often some form of chip deflector is arranged; e.g. in the form of beads or projections on the upper surface of the cutting insert and/or in the form of special elements on the tool, in particular clamps for retention of the cutting insert.
The modem high pressure cooling liquid technology aims at directing the cooling liquid jet into the substantially wedge-shaped space which is provided between the underside of the chip and the upper surface of the cutting insert at the point where the chip is distanced initially from the cutting insert. The intention is to form a so called hydraulic wedge between the chip and the upper surface of the cutting insert, which wedge should contribute to breaking up the chip and, as far as possible, to reduce the contact length of the chip along the cutting insert. A significant aim associated with introducing high pressure cooling liquid between the chip and the cutting insert is, of course, also to cool the chip and insert as effectively as possible,
A cutting insert intended for chip removing machining is previously known from WO 99/39853, which cutting insert has a chip deflector in the form of a number of small projections which are mutually spaced-apart by means of grooves into which high pressure cooling liquid may be injected with the purpose of shortening the contact length of the chip along the upper surface of the cutting insert. By means of these grooves, the high pressure cooling liquid may better penetrate beneath the chip at the same time as the surrounding projections aim at breaking up the chip in order to force the chip to deflect upwards/backwards as far as possible. Although this known cutting insert considerably improves the cooling and chip breaking effect in relation to older technology, no radical deflection of the chip in an upwards direction is effected. On the contrary, the chip tends to leave the upper surface of the cutting insert at a comparatively flat angle. This is something that in practice means that the chip may develop as a tangled skein.
The present invention aims at obviating the above-mentioned shortcomings in the previously known technology and at providing a cutting tool with an improved ability to control the chip, which has been cut free. Therefore, a primary object of the invention is to provide a cutting tool, which not only guarantees a good cooling but also an improved chip breaking ability.
One aspect of the invention relates to a cutting tool which comprises a front body part that forms a seat adapted to receive a cutting insert, a rear body part adapted to be detachably secured in a holder, and a plurality of liquid nozzles disposed rearwardly of the seat for emitting high pressure liquid jets. A first of the nozzles is arranged to direct its liquid jet toward a first target point for creating an hydraulic wedge between a cutting insert and a chip formed by the cutting insert. A second of the nozzles is arranged to direct its liquid jet toward a second target point disposed above the first target point for deflecting the chip upwards and backwards.
The invention also pertains to a metal cutting apparatus which includes the above-described metal cutting tool and a clamping unit in which the cutting tool is mounted.
Yet another aspect of the invention relates to a method of cutting a metal workpiece using a cutting insert, wherein a first liquid jet is directed from a first nozzle toward an upper surface of the cutting insert for creating an hydraulic wedge between the cutting insert and the chip, and a second liquid jet is directed from a second nozzle toward a target point disposed above the upper surface of the cutting insert to engage and deflect the chip upwards and backwards.